1. Field of the Invention
The present invention relates to the detection, by eddy currents, of typical defects on a product in relative movement with a detector, and more particularly to the detection of cracks on a slab or like product.
A slab as produced in a continuous casting installation may present on its surface, along its edges, defects in the form of cracks which it is important to locate before the subsequent treatment of the product.
2. Description of the Related Art
For detecting surface defects on a metal product in relative movement with a detector, it is known to use a process of detection employing eddy currents, process of the type whereby an alternating magnetic field is generated in order to provoke the circulation of eddy currents on the surface of the product, a signal representative of the variations of the eddy currents is collected by means of a differential sensor placed in the vicinity of the surface of the product, and the collected signal is demodulated by projection along an angle of adjustable phase in order to detect the disturbances introduced by the defects to be detected.
Detection of cracks on a slab by a process of this type is particularly difficult. In fact, in addition to the unfavourable operational conditions (particularly the temperature), there are numerous sources of noise, particularly the presence of surface irregularities (waviness or wrinkle formation), edge effects, random variations of the distance between sensor and product, etc . . .